supplementary materials

Redetermination of 4-nitrostilbene

In the title compound, C14H11NO2, the benzene rings are inclined to each other with a dihedral angle between their mean planes of 8.42 (6)°. The nitro group is almost coplanar with the attached benzene ring but is rotated about the C-N bond by 5.84 (12)°. This redetermination results in a crystal structure with significantly higher precision than the original determination [Hertel & Romer (1931). Z. Kristallogr.76, 467-469], and the intermolecular interactions have been established. In the crystal structure, molecules are linked by C-HO hydrogen bonds to generate C(5), C(13) and edge-fused R33(28) rings.

A great interest in the design of materials with potential applications in
photonic technology has been developed in recent years (Luo et al.,
2003; Vidal et al., 2008). Significant efforts have been
focused on
studying of design and the synthesis of organic molecules with potential
nonlinear optical response (NLO), improved optical transparency and thermal
stability (Park et al., 2004). A specific type of these
molecules
consists of electron donor and acceptor end groups interacting through a
conjugating segment. In a first stage of work in our group, the synthesis of a
stilbene molecule with nitro group with electron-withdrawing capacity as a
substituent in para position, is considered. In order to obtain
detailed structural information on the molecular conformation, its NLO
responses, its hydrogen bonded interactions and its supramolecular
arrangement, the crystal structure of p-nitrostilbene (I) was
undertaken.

Perspective view of the title molecule, showing the atomic numbering scheme, is
given in Fig. 1. The benzene rings are twisted out of the ethylene plane, as
defined by the torsion angles C3—C4—C7—C8 and C7—C8—C9—C14
therefore the benzene rings are inclined to each other showing a dihedral
angle between their mean planes of 8.42 (6)°. The nitro group is almost
coplanar with the benzene ring but it is rotated about the C—N bond with an
angle of rotation of 5.84 (12)°. If compared with the C7—C8 bond length to
the
expected value for a localized double bond [1.317 (13) Å, Allen et
al., 1987], the title distance shows some lengthening that is
indicative
of some π conjugation of the two benzene rings through the central ethene
bridge. The torsion angle between the benzene rings [C4—C7═C8—C9 =
178.48 (12)°] indicates a trans geometry between them. The crystal
structure of (I) is stabilized by weak C—H···O hydrogen-bonding interactions
[Nardelli, 1995, Table 1]. The formation of the framework can be
explained in
terms of three-one substructures. In the first substructure atom C2 in the
molecule at (x, y, z) acts as a hydrogen bond donor to
nitro atom O1 in the molecule at (-1/2 + x, 1/2 - y, 2 -
z)
so generating, by 21 screw axes, C(5) chains which are running along [100]
(Fig. 2). In the second substructure, atom C12 in the molecule
at (x, y, z) acts as hydrogen bond donor to nitro atom O2
in the molecule at (x, 1/2 - y, -1/2 + z) so generating
C(13) chains along [001] (Fig. 3). In the third-one
dimensional substructure atom C12 in the molecule at
(x, y, z) acts simultaneously as hydrogen bond donor to
atoms O1 in the molecule at (x, 1/2 - y, -1/2 + z) and
atom
O1 in the molecule at (3/2 - x, -y, -1/2 + z) so
generating
a chain of edge-fused with graph motif R33(28) rings along [001]
(Etter, 1990), [Fig. 4].

The synthesis of (I) was prepared by taking equimolar quantities of
benzyltriphenylphosphonium bromide (0.9600 g, 2.20 mmol) and
4-nitrobenzaldehyde (0.3355 g, 2.20 mmol). The mixture was stirred and it was
taken to reflux in dry THF in a nitrogen atmosphere at 273 K. 3.3 mmol of
potassium tert-butoxide was dissolved in 5 ml of t-butanol and this solution
was added drop to drop to the phosphonium mixture obtaining a change in the
color of the reaction mixture and completion of the reaction after two hours.
Single crystals suitable for X-ray analysis were obtained by evaporation at
room temperature using ethyl acetate as solvent.

The space group Pbca for p-nitrostilbene was assigned from the systematic
absences. All H-atoms were located from difference maps and then treated as
riding atoms [C—H = 0.93 Å and Uiso(H) = 1.2Ueq(C)].

Fig. 1. An ORTEP-3 (Farrugia, 1997) plot of the (I) compound,
with the
atomic labelling scheme. The shapes of the ellipsoids correspond to 50%
probability contours of atomic displacement and, for the sake of clarity, H
atoms are shown as spheres of arbitrary radius.

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes)
are estimated using the full covariance matrix. The cell e.s.d.'s are taken
into account individually in the estimation of e.s.d.'s in distances, angles
and torsion angles; correlations between e.s.d.'s in cell parameters are only
used when they are defined by crystal symmetry. An approximate (isotropic)
treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s.
planes.

RMF is grateful to the Spanish Research Council (CSIC) for the use of a
free-of-charge licence to the Cambridge Structural Database (Allen,
2002). RMF
also thanks the Universidad del Valle, Colombia, for partial financial
support.